Embodiments of the present invention relate generally to photovoltaic (PV) arrays and, more particularly, to systems and methods for collecting performance data on PV arrays for condition monitoring thereof, so as to enable accurate detection of PV array degradation or other performance related issues.
PV power systems are power systems that employ a plurality of solar modules to convert sunlight into electricity. PV systems include multiple components, including photovoltaic modules, mechanical and electrical connections and mountings, and means of regulating or modifying the electrical output. One common arrangement in PV systems is for several PV modules to be connected in series to form a PV string, with multiple PV strings in a PV system then being combined in parallel to aggregate the current in a PV array. The PV modules generate direct current (DC), with the level of DC current being primarily dependent on solar irradiation and the number of solar modules used. The level of DC voltage is primarily dependent on the arrangement of the PV modules and operating temperature. When alternating current (AC) power is desired, an inverter is used to convert the DC energy from the array into AC energy, with such AC energy being suitable for transfer to a power grid.
It is recognized that there are several system design and component challenges associated with the operation of PV power systems, including system monitoring and understanding of system performance. Furthermore, it is recognized that PV arrays degrade over time and lose power and that PV arrays can also have failures either in the module itself or in the wiring and connections in between modules. With respect to system monitoring, such monitoring in existing PV power systems is often performed by monitoring hardware and software in the inverter that collects and analyzes data during operation of the PV modules in existing natural operating conditions. For example, current measurements can be acquired via current sensors either in the inverter or separate to the inverter. These values can be sampled periodically (e.g., sampling rate of 15 minutes) and sent to a central service for analyzing by an algorithm, with the algorithm identifying degraded strings or degraded groups of strings (depending on current sensor locations) by data-mining current measurement with values lower than the average/typical current.
While this collected data can provide useful points of data for identifying degradation of the PV arrays and/or failures in the PV arrays or wiring/connections of the PV system, it does not provide accurate performance curves that would enable a detailed diagnosis of the PV system condition. Additionally, the data collected via traditional means by existing monitoring systems is not calibrated or collected under defined conditions. This results in performance data this is not sufficiently accurate or useful to understand PV plant performance.
It would therefore be desirable to provide a solution for a PV system that controls the data collection such that calibrated conditions are applied. It would also be desirable for the monitoring solution to force the voltage conditions to specifically develop full operating curves rather than discrete operating points.